RE: GRO aggregation

From: Eric Dumazet [eric.dumazet@gmail.com]
Sent: Tuesday, September 11, 2012 9:33 PM
To: Shlomo Pongratz
Cc: netdev@vger.kernel.org
Subject: Re: GRO aggregation

On Tue, 2012-09-11 at 16:45 +0300, Shlomo Pongartz wrote:

Hi,

I’m checking GRO aggregation with kernel 3.6.0-rc1+ using Intel ixgbe
driver.
The mtu is 1500 and GRO is on and so are SG and RX checksum.
I ran iperf with default setting and monitor the receiver with tcpdump.
The tcpdump shows that the maximal aggregation is 32120 which is 21 * 1500.
In the transmitter side tcpdump shows that TSO works better (~64K).
I did a capture without GRO enabled to see if there was a difference
between any flag
of any two consecutive packets that forced flushing but didn't find
anything.
Is the GRO aggregation can be tuned.

It might mean NAPI runs while about 21 frames can be fetched at once
from NIC.

If receiver cpu is fast enough, it has no need to aggregate more segment
per skb.

Is LRO off or on ?

GRO itself has a 64Kbytes limit.

Hi Eric.

I disabled the LRO. I actually tried the all the 4 options and found that LRO, GRO, LRO+GRO gives the same results for ixgbe w.r.t aggregation size (didn't check for throughput or latency).
Is there a timeout that flushes the aggregated SKBs before 64K were aggregated?

Shlomo